1. Field of the Invention
The present invention relates to a metal shield (Faraday Cage) for an image intensifier which shield also provides a bypass capacitor for a power lead coupled to said image intensifier.
2. Description of the Prior Art
An image intensifier is used to amplify the brightness of faint image of an object to enable one to obtain a clearer view of the object. Such devices have been widely employed both commercially and by the military in various applications. An important use of the image intensifier is in night vision equipment. Night vision equipment is frequently employed by the military as the principal means of maintaining necessary visual awareness of the environment during nighttime operations. For example, a helicopter pilot may be required to pilot his aircraft in the dark and at low altitudes with night vision goggles being the primary means for seeing the landscape. Accurate visual awareness is critical in situations of this nature. Electromagnetic interference (EMI) can interfere with the operation of image intensifiers. If an unshielded image intensifier is used in an environment having appreciable EMI, brightness changes in the output image can result, thereby depriving the wearer of accurate visual data, and therefore creating an unacceptable risk. Thus the image intensifier should be adequately shielded against EMI. An example of prior art shielding can be had by referring to a U.S Pat. No. 4,924,080 awarded in May, 1990 to J. Caserta, W. Mims, J. Bowman and J. Reed, filed on Jul. 5, 1988, and entitled ELECTROMAGNETIC INTERFERENCE PROTECTION FOR IMAGE TUBES, and assigned to the assignee herein by the inventors herein. The aforesaid application describes a shielding device for an image intensifier which employs a Faraday Cage for surrounding the intensifier tube and its power supply and includes a set of capacitors for capacitively bypassing the incoming power leads to the tube's power supply. Although of great utility, the foregoing invention requires capacitors which occupy significant space and require relatively complex and expensive assembly. Further, the foregoing invention provides a limited frequency blocking range because the capacitors are descreat rather than uniformly distributed and the descreat capacitor exhibit inductance at high frequencies. Naturally, it is preferable for intensifier equipment to be of minimum size, weight, complexity and cost, and to have EMI shielding means that are maximally effective.
The present invention provides improved EMI shielding and improved power lead capacitor bypassing for an image intensifier via a simple, economical device. The device to be described is also compatible with and retrofitable to existing image intensifiers.